april fools storm
-
Upload
ceciliamreeves -
Category
Documents
-
view
220 -
download
0
Transcript of april fools storm
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 1/9
April Fool’s Day Storm
1. Incipient Disturbance (March 31,1997)
On March 31st at 00z-06z
there was an initial lowover Virginia.
There was also a jet strea
at 200mb to the west of
the Low and cold fronts,
over Tennessee, because
the strong thermal gradi
The indirect circulation is
corresponding with the
surface low and the area
maximum PVA anddivergence.
It can be seen on the IR
that a baroclinic leaf was
formed.
Based on the 500mb steering method of forecastin
is assumed that the low would move towards the
East, because of the height gradients being the
tightest just south of the low.
There is a subtropical jet that is bringing moisture
into the area of interest (towards the polar). This i
what looks to make this into a high precipitation
system.
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 2/9
Rapid Development Stage (15z March 31, 1997)
It is notable that due to the temperature
gradient over the Atlantic brought by the
subtropical jet has created a warm front over
the Atlantic, off the coast of Virginia.
If the low moves as predicted above
(500mb steering) it should join with the warm
front to strengthen the disturbance.
The pressure minimum deepened slightly which is causing the cyclonic flow to intensify.
The vorticity has increased at the base of the trough as it moved east due to the increase
in curvature and shear. This increased the PVA and divergence on the downstream side
of the trough.
Warm air advections enhanced the dipole in vertical motions.
The increased thermal advections are lowering the heights upstream and increasing the
heights downstream
A comma cloud is beginning to form because of the divergence behind the cold front.
The surface cyclone should follow the warm front, which is the largest thickness gradient,
so it should go towards the East and a little north.
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 3/9
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 4/9
Mature Stage (18z March 31, 1997)
The limiting streamine is
becoming evident (can be
seen over Pennsylvania and
Delaware)
There is also evidence of an
enhanced warm conveyor
belt in the Atlantic (off the
coast of the Carolinas) and
cold conveyor belt coming
from the Atlantic.
At this point in the cyclone life cycle, the cloud and precipitation areas have
expanded, and the cyclone is at maximum intensity.
The surface map shows that the system is already occluding but, by analyzing
the upper air charts, the trough is not vertically stacked yet, which signals that
although this system is very close to decay at 18z it has not occluded yet.
In this stage both the vorticity and advections are at their maximum, and so isPVA.
Using 500mb steering the gradient will make the low go north, which will
weaken it, leading to the decay stage.
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 5/9
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 6/9
Decay (00z April 1, 1997)
In this stage the cyclone is vertically stacked and a secondary speed maximum has formed over the
downstream ridge so there is no more PVA being fed into the low (occlusion has occurred).
The tail of the comma cloud narrows and the head expands. As seen in the satellite image the cold
air is beginning to cut off the low so that there is no longer warm air advection to the initial low.
Because the cyclone is weakening it is going to go north, and develop a secondary low following the
warm front where thermal and vorticity advections are still strong.
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 7/9
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 8/9
8/7/2019 april fools storm
http://slidepdf.com/reader/full/april-fools-storm 9/9
The “April Fool’s Day Storm” was a fast moving and short lived snowstorm that affected so uthern
New England in 1997. The storm brought damaging winds and record snowfall to a large portion of
the area. Areas saw snowfall totals as high as 36” from this storm.
References
200mb charts, weatherchannel surface maps and satellite images:
http://www.njfreeways.com/weather/1997/31-Mar-97.html
http://weather.unisys.com/archive/
4-panel charts:
http://www.meteo.psu.edu/~gadomski/NARR/1997/us0331.php
weather maps:
http://nomads.ncdc.noaa.gov/ncep-charts/archives/19970331
GOES satellite image:
http://dcdbs.ssec.wisc.edu/inventory/image.php?sat=GOES-8&date=1997-03-
31&time=19:02&type=Imager&band=1&thefilename=goes08.1997.090.190144.INDX&coverage=CONUS
&count=1&offsettz=0
Summation of the storm:
http://ccams.eas.cornell.edu/ithacation/ith_feb03.pdf